RagnarLunchbox

As I said, the router's WWAN IMEI is a bit like a MAC address that is bound to a hardware brand and type. But unlike simple MAC spoofing, you cant bypass that without some very advanced spy level hack skills and that's can even be a criminal offence in some countries. (IMEI numbers are involved in network and cell tower authentication.) The carrier expects a link with a device that has the IMEI of a voice handset - and the Netgear cant do this.

Your carrier might work with the Netgear just fine, but that will only due to how motivated the carrier is to dectect and police this breach of their terms. You can buy the Netgear, but there is a risk that you'll get cut. The only way to defeat this reliably is via the method I've given you, which is akin to exploiting a technical loophole.

The spare phone as a modem is the only foolproof way unfortunately.

With a router, devices connected behid this creates an an extra hop and this can be detected in the TTL, but you mileage may vary if you put a sim in a WWAN enabled router. It might work or it might not.

I've tried a number of methods with different carriers. Some dont limit this sort of thing via technical surveileance, they just deploy an acceptable use policy. (but these are typically the carriers that give you unlimited data BUT with a maximum speed cap) The faster the link, the more likely you will encounter proactive surviellance.

EDIT: This below usb modem link is also a voice enabled device that you can build a raspi phone out of, and it also can recieive SMS, making it likely it reports as a voice enabled device, which is what carriers usually stipualte. I've had no issues with multiple SIM plans in it.

I use this IOT type usb industrial modem plugged into my OpenWRT router as my failover link which is viraully plug and play in linux, The benefit with this is I can also use this modem on other professional study projects for testing and its much cheaper that a spare phone. Its just another cheaper option to think about.

https://www.waveshare.com/sim7600g-h-4g-dongle.htm

Yes, but you can work around any imitations if you are clever and understand their means of detection.

The carrier can tell whether the sim card is in a phone vs tethered to a router and shared. They can track this in two ways.

1. via the IMEI number of the phone, some carriers will detect if the sim is not in a voice device, so placing the sim in a 4/5G enabled router may be esily tracked & detected.
2. Tethered to a router via USB can be detetected via the TCP/IP TTL value. With every hop on a netowrk, the TTL of packets is reduced in increments. The carrier can look at the TTL it expects vs the TTL is sees t odetermin that there are more hops downstream of the phone, which will be added by a router.

But this can all be defeated

You simply tether your phone to a router over USB as if it is a WWAN interface. OpenWRT is a great router OS to do this (I have done this with both iphone and adroid, though android is simplest)

AFrom there, with the WWAN setup up, all you need to do is re-increment the TTL by 1 at the router to compensate for the extra hop and your router is invisible to the carrier.

This is done in the OpenWRT firewall custom config: (here is a example I am using in my config, - "wan_iphone" is the usb tethered phone interface name)

iptables -t mangle -I POSTROUTING -o wan_iphone -j TTL --ttl-inc 1

Your carrier wil have no idea!

Even though I have a lifetime LastPass subscripion I still choose to pay the $10 bucks and stay with Bitwarden not just becuse I wanted the yubikey support, its also just so simple to use and I love its simplicity. Its also polite and does not bring any extra bloatware. Its really quite good value. It just does its job really nicely